It's an expression millions have people have used in context with sex, laughter, and life in general.
A lot of us say or write things like what you just did. You're not a psychopath! It just means the lee is going to experience an overload of sensations. Notice no one ever says... "I've going to tickle you to birth." Though some might say: "You'll be reborn". Meaning you will understand a bliss or higher ground. An awakening. They call orgasms "the little death". Sex and death have been intertwined forever. Here are some quotes throughout history. I think you have heard Laughter, Sex, Orgasms, and everyday life/feelings: all be related in some way to death over the years. And general quotes that people say every day. And ultimately what so many of us has said MEANS: You will be happier (or laugh) more than you have ever experienced in your entire LIFE. You might even "See God". Or: "Meet the Devil". The mind and body get taken to such a pleaurable (or torturous) place with Tickling. Or BDSM pain. (Whippings, spankings etc) It is a journey the body and mind go through towards orgasm. Or head space. Or even meditation.
"If you become silent after your laughter, one day you will hear God also laughing, you will hear the whole existence laughing — trees and stones and stars with you."— Osho
My family loves my boyfriend as much as I do, so they were just tickled to death to hear that we're getting married."
" Your mother is really tickled to death that you've decided to go to her alma mater."
“And is death not the ultimate orgasm, a return to that otherworldly ether, whose very origins were indeed a Big Bang, the ultimate explosion, the supreme chaos, whose resonance is the vibration we constantly seek to reproduce in everything we do.”
― Lydia Lunch
These next 2 quotes from Osho I post here because not everyone believes death is the end. But the beginning...
"Death is the most misunderstood phenomenon. People have thought of death as the end of life. That is the first, basic misunderstanding." Osho
“Death is not the end, but the beginning of a new life. Yes, it is an end of something that is already dead. It is also a crescendo of what we call life, although very few know what life is. They live, but they live in such ignorance that they never encounter their own life. And it is impossible for these people to know their own death, because death is the ultimate experience of this life, and the beginning experience of another. Death is the door between two lives; one is left behind, one is waiting ahead." Osho
BDSM quotes:
"Lust's passion will be served; it demands, it militates, it tyrannizes." -Marquis De Sade
"Your body is the church where Nature asks to be reverenced."- Marquis De Sade
"Crime is the soul of lust. What would pleasure be if it were not accompanied by crime? It is not the object of debauchery that excites us, rather the idea of evil."- Marquis De Sade
“Fear can be a potent aphrodisiac.”
― Kele Moon, Beyond Eden
"Right on the edge of fear, is where trust would grow". - Cherise Sinclair
"S&M is as psychological as it is physical and sexual, Zach. Imagine being as deep inside a woman’s mind as you are inside her body.”- Tiffany Reisz
“I do not want to be the leader. I refuse to be the leader. I want to live darkly and richly in my femaleness. I want a man lying over me, always over me. His will, his pleasure, his desire, his life, his work, his sexuality the touchstone, the command, my pivot. I don’t mind working, holding my ground intellectually, artistically; but as a woman, oh, God, as a woman I want to be dominated. I don’t mind being told to stand on my own feet, not to cling, be all that I am capable of doing, but I am going to be pursued, fucked, possessed by the will of a male at his time, his bidding.”
― Anaïs Nin
Read this:
https://writingexplained.org/idiom-dictionary/tickled-to-death
And this- "La Petite Mort"
https://en.m.wikipedia.org/wiki/La_petite_mort
Also check this out:
http://www.thesaurus.com/browse/tickled to death
If you truly want someone to die through tickling. Yes get counseling. But... if you don't (which is pretty obvious in what you have written here) and you understand what I have shown you here.... you are FINE. Please stop overthinking this. lol